The present invention relates to an electrostatic recorder provided with an electrostatic latent image measuring instrument, and, more particularly, to an electrostatic recorder controlled in accordance with results of measurement of an electrostatic latent image, and an electrostatic latent image measuring instrument capable of directly measuring an electrostatic latent image formed on a photosensitive substance.
There is no conventional electrostatic recorders having electrostatic latent image measuring means mounted thereon. In general, the exposure, the development bias and the like have been determined at predetermined design values having sufficient allowance, and the fine adjustment has been made by an operator for every device. It is known that an electrostatic recorder controls an electrostatic charge system, an exposure system and a development system by a fatigue correction program based on the number of printed sheets as fatigue correction of a photosensitive substance (JP-A-62-27390). It is also known that an electrostatic recorder determines the life of a photosensitive substance with the number of printed sheets and the like (JP-A-62-505).
Additionally, ion motion type, a DC amplification type, a revolving sector type, an electro-optical effect type, and an electric power type have been proposed (Kazutoshi Asano: Electric Field and Potential Measuring Method in Electrostatic Engineering, Journal of Institute of Electrostatic Engineers, 10, pp. 205-212 (1986)), as a method of measuring an electrostatic latent image. Since an electrostatic latent image on a photosensitive substance has a size of several hundreds to several tens .mu.m, an electrostatic latent image measuring technique having sufficiently high resolution is required to measure the distribution of the electrostatic latent images. In order to improve resolution, the area of a measuring electrode has to be small, and the measuring electrode and the photosensitive substance have to be close to each other. Several reports in which an electrostatic latent image has been measured by using an electrode having a very small measurement area have been proposed. (Mitsuru Matsui: Very Small Area Surface Electrometer, journal of Institute of Electrostatic Engineers, 10, pp. 217-224 (1986)). A report also has proposed a measurement of the electrostatic latent image by the electron microscope with using measuring electrode (G. F. Fritz, D. C. Hoesterey and L. E. Brady: Observation of Xerographic Electrostatic Latent Images with a Scanning Electron Microscope, Appl. Phys. lett. 19, pp. 277-278 (1971)).
Since there has been no means for observing an electrostatic latent image in an electrostatic recorder, it is difficult to carry out the fine adjustment so that the device is suited to individual photosensitive substance, and it is also difficult to fully demonstrate the performance of the photosensitive substance in the case of the conventional electrostatic recorder. Further, it is impossible to accurately determine the life of a photosensitive substance since the electrostatic latent image cannot be observed whether the latent image is present or not.
Furthermore, no consideration has been given so as to measure an electrostatic latent image in an electrostatic recorder in the conventional electrostatic latent image measuring instrument in which the area of a measuring electrode is small. There is eccentricity and the like in a photosensitive drum on an electrostatic recorder, which has made it impossible to have a measuring electrode come close to a photosensitive substance at a very small distance. Moreover, the electric potential of an electrostatic latent image on a photosensitive substance sometimes reaches near 1 KV, thus causing a problem of discharge occurring when the measuring electrode is brought close to the photosensitive substance.
Further, above-mentioned the conventional devices for measuring an electrostatic latent image using the electron microscope are incapable of measuring a latent image on a photosensitive substance of the electrostatic recorder due to special measuring environment.